The effect of advancing age on bone mineral in old world primates is not well established. The purpose of this study was to longitudinally monitor skeletal changes in old female rhesus monkeys by dual-energy x-ray absorptiometry (DXA). Initial DXA scans of the lumbar spine, total body, total hip, and radius (distal and 1/3 sites) were performed on twenty female rhesus monkeys (age 21-35 years) and were repeated 9-12 months later. Animals were considered postmenopausal based upon the absence of observed menses in the preceding two years. Data analysis was by Student's T-test. At baseline, no bone mineral density (BMD) difference was observed between pre- and postmenopausal groups at any skeletal site. BMD did not decrease at any site in either the pre- or postmenopausal group. At the 1/3 radius site, BMD tended to increase in the premenopausal group (Table). Premenopausal Postmenopausal DXA sites baseline follow-up baseline follow-up Total body .799 (.015) .794 (.015) .814 (.019) .817 (.015) Lumbar spine .663 (.033) .661 (.032) .718 (.045) .745 (.043) Total hip .827 (.063) .823 (.066) .957 (.056) .898 (.058) Distal radius .274 (.016) .276 (.015) .248 (.001) .253 (.011) 1/3 radius .407 (.017) .413 (.018) .407 (.015) .399 (.017) data presented as mean BMD (g/cm2) q SEM different than baseline = p < .05 In conclusion, in both pre- and postmenopausal rhesus monkeys, no demonstrable bone loss was observed at any skeletal site over a 9-12 month period. While estrogen-depletion bone loss is well established in old world primates, this suggests that "age-related" bone loss may not occur. As such, female rhesus monkeys may be an inadequate model of the aging human skeleton. Dietary manipulation may be required to more accurately mimic the human condition.